Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2008
Publication Date: 11/18/2008
Citation: Yoshinaga, N., Aboshi, T., Abe, T., Nishida, R., Alborn, H.T., Tumlinson, J.H., Mori, N. 2008. Active role of fatty acid amino acid conjugates in nitrogen metabolidm by Spodoptera litura larvae. Proceedings of the National Academy of Sciences. 105:18058-18063.
Interpretive Summary: Volicitin, and related fatty acid amino conjugates (FACs) have, since their discovery by ARS scientists in the chemistry group at CMAVE in Gainesville, Fl, been well documented and studied worldwide for their role in plants induced defensive responses to insect herbivory. However, the studies of FACs role in insect physiology have been minimal. By utilizing C14 labeling eperiments ARS scientist at CMAVE in Gainesville in collaboration with scientist at Penn State University and Kyoto University found that FACS play an active and important role in glutamine assimilation in the gut of Spodoptera litura and that FACs also play an important role in the glutamic acid to glutamine conversion in the insect gut. Furthermore, FACs also appear to function as a short term storage of glutamine which is a key component of nitrogen metabolism in insects. By understanding the function of FACs in the insect metabolism we might find new ways to control pest insects.
Technical Abstract: Since the first fatty acid amino acid conjugate (FAC) was isolated from regurgitant of Spodoptera exigua larvae in 1997 [volicitin: N-(17-hydroxylinolenoyl)- L-glutamine], their role as elicitors of induced responses in plants has been well documented. However, studies of the biosyntheses as well as the physiological role of FACs in the insect have been minimal. By utilizing 14C-labeled glutamine, glutamic acid and linolenic acid in feeding studies of S. litura larvae, combined with tissue analyses, we found glutamine in the midgut cells to be a major source for biosynthesis of FACs. Furthermore, 20% of the glutamine moiety of FACs was derived from glutamic acid and ammonia through enzymatic reaction of glutamine synthetase (GS). To determine if FACs improve GS productivity, we studied nitrogen assimilation efficiency of S. litura larvae fed on artificial diets containing 15NH4Cl and glutamic acid. When the diet was enriched with linolenic acid, the nitrogen assimilation efficiency improved from 40% to more than 60%. In the lumen the biosynthesized FACs are hydrolyzed to fatty